Abnormal behavioral is one of the major causes of institutionalization in patients with Alzheimer's disease (AD). Abnormal behaviors range from sweet-food craving to anger, hostility and/or aggression, and can occur at any time in the course of the disease, regardless of the severity of memory loss. It has been postulated that some abnormal behaviors are related to abnormalities in the brain serotonin axis. Recently, clinically applicable tests of brain serotonin function have become available. Stimulation of the brain serotonin system results in increased production of prolactin, which can be readily measured in serum. This response can be produced by fenfluramine or buspirone, both FDA approved drugs. The magnitude of the prolactin response is related to serotonin system integrity. We propose to study 40 subjects with probable Alzheimer's disease (NINCDS/ADRDA criteria). All subjects will receive fenfluramine and buspirone stimulation tests, and the prolactin response will be measured. We will then determine if prolactin response is related to specific abnormal behaviors which have been linked with serotonin functioning in previous studies: agitation, aggression, depression, suicidal ideation, sleep disturbance, and preference for sweet foods. In this manner we will evaluate the relationship between central serotonin functioning and specific behaviors that can create management problems in AD. If serotonin dysfunction can be linked to behavior problems, then a rational basis would be available for further studies using drugs that influence serotonin functioning to manage problematic behavior.